Team K is punting after a safety from K20.

If the PR touches the ball at the 4 yard line and it continues to go into the endzone, the PR picks it up and is tackled in the endzone, is it a touchback or a saftey?

Pretty sure this is a touchback, unless PR had possession. Doesn't sound like he did by your description.

No posession at all, just a muff. So this would be a touchback correct?

The kick hasn't ended, any time a kick goes into R's EZ we have a TB.

Incorrect. Unlike NFHS, impetus ("force") can be considered on kicks entering R's endzone at this level. If the covering official determines that R provided new impetus to the ball, it is a safety. If the muff did not provide new impetus, it is a touchback. When in doubt, there was not new impetus.

Remember, this applies to a free kick. On a scrimmage kick punt the same would be true if R touched the ball. However, a new rule this year on scrimmage kicks is similar to the Fed. rule:
on a scrimmage kick that is untouched by the receiving team and crosses the receiving team's goal line from the impetus of the kick, the ball is dead as soon as it touches the ground or a member of the kicking team on or behind the receiving team's goal line.

Hope that clears things up ;)
Jonathan

You're right, I thought we were talking NFHS, didn't realize it was NFL.

At least we got it right before the next play, right? ;)
It wasn't real obvious that he was referring to NFL--it was only in the thread name. I've done that before; unless someone specifically states otherwise, I read situations on here as if they're NFHS.

Jonathan